Yeah I take your point; you would need to have readied someone in the window where you commit characters to the quest, before drawing the treachery.
Maybe throw in some Hobbit Ponies? (Galadriel and/or Rosie would avoid the whole issue as well.)

I'd have to Google for it. (The Golum escape test in shadows of mirkwood has a similar mechanic and ruling, if I recall correctly, so I may be getting things crossed! In both cases: actions are allowed immediately prior to the test.)

I think there was a clarification from a developer that something to the effect that "a fortitude test creates its own window for player actions immediately preceding the test"
(We had to look it up, but it feels to me that it was intended to work that way.)

You hopefully can burn 3 golden hairs at the start (threat reduction from boons still works beyond 1.)
Starting in your teens, especially with Galadriel, you can last a while; the whole mission is only about 5-6 rounds.

I explained it badly; we had done the "Frodo" missions with secrecy decks. When we got to Mountain of Fire, we adapted them specifically for the mission.
The key element of the quest seemed to be managing threat; keeping it mostly in the 20s was a great help.
To do this, we went with very few allies. Some effects are really punishing with lots of characters.
We were fortunate to have used Dunhere most of the saga; with +1 attack and ignoring 2 armour, he could clear the staging area quickly. ( He came in huge in Bree and again in the crossroads, straight shot a Mumak.)
With Galadriel/Rosie, spare cloaks, readying effects, we almost always had someone with 7+ willpower to do a fortitude test. (There is a window for player actions before the test!)
Stuff to deal with locations is a big help as well.
Hopefully that clarifies what worked for us.

No, we didn't stay in secrecy the whole time, or even past turn 1! (Might be possible in a two hero deck, but not with 3.)
Rosie, Strider, Sword Thane, Fast Hitch, Celebrian's Stone was the core of one deck.
Dunhere clearing enemies in staging was the other deck. (Dunhere had an attack boon.)
Both decks had very few allies.
Spare Cloak actually was fairly useful.

Secrecy and keeping the ally count down helped us a lot. Sam, Pippin, Rosie and Galadriel on one team, Eowyn, Glorfindel, Dunhere on the other.
(I think it actually works better to do Mountain of Fire before the Black Gate; changes the feel of that mission, to where you need to hold out a certain number of turns.)

Radagast would be awesome and the final artifact is OBVIOUSLY the "Star of Elendil"
Bold prediction: there will be a secret mission included with the last pack that involves time travel, the "Dunland Trap", returning the artifact back where it came so that Aragorn can find it during the sack of Isengard so the space time continuum doesn't collapse in on itself.

Fatty and Pippin need:
Hobbit Sense: 1 cost - spirit - after your threat is raised by a player card, discard Hobbit Ferocity to grant each Hobbit hero you control +1 attack, defense, willpower until the end of the phase. Reduce your threat by 1.

I think it is more that his threat is too high for his ability, and the cost better suited to Leadership or Gondor. He has synergy with a Elrond and Treebeard, but you aren't going to run the three of them together outside of specific missions (Shadow and Flame?)
Make him 9 cost: 3-2-1-3 stats - "discard a card from your hand to heal a point of damage."
It's not that he is bad in a vacuum, but he doesn't really complent other heroes.

Grimbeorn is certainly a stand-out, but Dain, Haldan and Bard are all really solid and open up new playstyles. I think the support for existing decks ( silvan, eagles ) has been good, and the addition of cards like the boots really help multiplayer play. Really been pleased with the new options; if anything, Grimbeorn is a bit too much power-creep (which reduces diversity in decks!)

There is a thematic deck that almost creates itself:
Bilbo - Gandalf - Thorin
Glamdring - Sting - Orcrist - Magic Ring
The dwarf allies
For our scenario, "Gandalf" is a captive in Dol-Guldur and Thorin recruits Bilbo to rescue him and following that they learn Golum was a prisoner too and head off in pursuit.
maybe I am thinking about it the wrong way .... but it feels like "That SHOULD work"